The COVID-19 pandemic has highlighted the need for a proper risk assessment of respiratory pathogens in indoor settings. This paper documents the COVID Airborne Risk Assessment methodology, to assess the potential exposure of airborne SARS-CoV-2 viruses, with an emphasis on virological and immunological factors in the quantification of the risk. The model results from a multidisciplinary approach linking physical, mechanical and biological domains, enabling decision makers or facility managers to assess their indoor setting. The model was benchmarked against clinical data, as well as two real-life outbreaks, showing good agreement. A probability of infection is computed in several everyday-life settings and with various mitigation measures. The importance of super-emitters in airborne transmission is confirmed: 20% of infected hosts can emit approximately two orders of magnitude more viral-containing particles. The use of masks provides a fivefold reduction in viral emissions. Natural ventilation strategies are very effective to decrease the concentration of virions, although periodic venting strategies are not ideal in certain settings. Although vaccination is an effective measure against hospitalization, their effectiveness against transmission is not optimal, hence non-pharmaceutical interventions (ventilation, masks) should be actively supported. We also propose a critical threshold to define an acceptable risk level.

BACKGROUND: Indoor aerosol transmission of SARS-CoV-2 has been widely recognised, especially in schools where children remain in closed indoor spaces and largely unvaccinated. Measures such as strategic natural ventilation and high efficiency particulate air (HEPA) filtration remain poorly implemented and mask mandates are often progressively lifted as vaccination rollout is enhanced. METHODS: We adapted a previously developed aerosol transmission model to study the effect of interventions (natural ventilation, face masks, HEPA filtration and their combinations) on the concentration of virus particles in a classroom of 160 m3 containing one infectious individual. The cumulative dose of viruses absorbed by exposed occupants was calculated. RESULTS: In the absence of interventions, the cumulative dose absorbed was 1.5 times higher in winter than in spring/summer, increasing chances of indoor airborne transmission in winter. However, natural ventilation was more effective in winter, leading to up to a 20-fold decrease in cumulative dose when six windows were fully open at all times. In winter, partly opening two windows all day or fully opening six windows at the end of each class was effective as well (2.7- to 3-fold decrease). In summer, good ventilation levels could be achieved through the opening of windows all day long (2- to 7-fold decrease depending on the number of windows open). Opening windows only during yard and lunch breaks had minimal effect (≤1.5-fold decrease). One HEPA filter was as effective as two windows partly open all day in winter (3-fold decrease) whereas two filters were more effective (5-fold decrease). Surgical face masks were very effective independently of the season (8-fold decrease). Combined interventions (i.e., natural ventilation, masks, and HEPA filtration) were the most effective (≥25-fold decrease) and remained highly effective in the presence of a super-spreader. INTERPRETATION: Natural ventilation, face masks, and HEPA filtration are effective interventions to reduce SARS-CoV-2 aerosol transmission. These measures should be combined and complemented by additional interventions (e.g., physical distancing, hygiene, testing, contact tracing and vaccination) to maximise benefit.

The characterization of commercial-grade power transistors upon high levels of particle irradiation is required to enable radiation tolerant LED power supplies for the new luminaires of CERN accelerator tunnels, which represent a harsh environment for semiconductor devices. This work describes the effects of 24 GeV/c proton irradiation on commercial GaN hybrid-drain-embedded gate injection transistors (HD-GITs) after a fluence of 5.9 x 10(14) p/cm(2). Measurements of drain leakage current, threshold voltage and I-ds - V-ds curves show that only a minor variation occurs in the electrical properties of GaN HD-GITs after the considered fluence; for example, an average increase of approximate to 11-13 mV is found in the threshold voltage upon irradiation. We also put forward a physical explanation of the observed degradation caused by proton irradiation; in particular, the electron drift velocity in the 2DEG channel at high electric fields appears to decrease due to a radiation-induced increase in phonon relaxation rate. Finally, an AC/DC LED power supply with current control using GaN HD-GITs is proposed for the new luminaires of CERN tunnels, meeting the requirements in terms of radiation hardness and light quality.

This paper describes the board level testing of a linear power supply based on SiC Junction Barrier Schottky diodes and GaN Hybrid Drain embedded Gate Injection Tran-sistors in a 186 MeV proton beam to evaluate the potential sensitivity to SEEs. The GaN components of the power supply have been individually tested against cumulative radiation dam-age in passive mode (i.e. unbiased) up to a 1 MeV(Si) neutron equivalent fluence of $3.4\times 10^{14}$ n/cnr 2 , It is planned for the lighting system to be in the off state during normal accelerator operation, however the potential consequences of accidental or inadvertent powering the lighting must also be understood. If tolerant to SEEs, the power supply can also be potentially used as a current-controlled power supply for other applications in harsh radiation environments. In this context, board level testing is used to rapidly confirm the radiation hardness and expected performance designed into the power supply. Boards were irradiated in a uniform field and no failures were observed on test devices up to the maximum fluence of $1.0\times 10^{11}\mathrm{p}/\text{cm}^{2}$ .

We report the effects of high-energy (23 GeV) proton irradiation at large fluences on packaged high-power GaN-based white light-emitting diodes with YAG:Ce phosphors. From optical and electrical measurements, we assume that proton irradiation degrades only the GaN LED die up to fluences of at least 2 × 1014 p/cm2, and we demonstrate that it produces nonradiative recombination centres which increase the leakage current and diminish the carrier density in the quantum wells and hence the output optical power. We also propose for the first time a model correlating optical and electrical degradation induced by radiation.

An irradiation campaign was conducted to provide guidance in the selection of materials and components for the radiation hardening of LED lights for use in CERN accelerator tunnels. This work describes the effects of gamma-rays on commercial-grade borosilicate, fused quartz, polymethylmethacrylate, and polycarbonate samples up to doses of 100 kGy, to qualify their use as optical materials in rad-hard LED-based luminaires. In addition, a Si bridge rectifier and a SiC Junction Barrier Schottky diode for use in power supplies of rad-hard LED lighting systems are tested using 24 GeV/c protons. The physical degradation mechanisms are discussed for each element.

This paper summarises progress made towards the radiation hardening of LED emergency luminaires for evacuation and emergency response within the underground areas of the CERN accelerator complex. The objective has been to radiation harden existing Commercial Off-The-Shelf (COTS) emergency luminaires to maximise lighting performance, without compromising IEC 60598-2-22 compliance. A systems level approach has been adopted, leading to the development of a diode bridge based AC/DC power converter. Modified COTS luminaires including this converter design have been irradiated (to 100 kGy TID using a Cobalt-60 source), with results of a subsequent photometric analysis presented. Following encouraging tests results, a reference design for the power converter has been released under the CERN Open Hardware License to encourage manufacturer adoption. The paper concludes with areas of interest for future research in further improving the radiation hardness of LED emergency lighting for accelerators with detailed studies at the component level for high power white LED devices and associated optical components.

Presents a collection of slides covering the following topics: distributed PV systems, network topology, intrinsic resilience and data analysis.

The LHC Injectors Upgrade project (LIU) has been initiated to improve the performances of the existing injector complex at CERN to match the future requirements of the HL-LHC (High Luminosity LHC). In this framework, theProtonSynchrotron(PS) will undergofundamental changes for many of its main systems: the injection energy will be increased to reduce space-charge effects, the transverse damperwill be improvedto cope with transverse instabilities, and the RF systems will be upgraded to accelerate higherbeamintensityand brightness. Thesehardware improvements are triggered by a series of studies meant to identify the most critical performance bottlenecks, like space charge, impedances, longitudinal and transverse instabilities, as well as electron-cloud. Additionally, alternative production schemes for the LHC-type beams have been proposed and implemented to circumvent some of the present limitations. A summary of the most recent advances of the studies, as well as the proposed hardware improvements is given.